This object is accomplished in accordance with the invention in a non-return valve of the above-mentioned type wherein the hollow cone has an apex angle between about 140.degree. and 160.degree., and the membrane is a flat disk of an elastomer, having a central circular aperture resiliently biased against the hollow cone. It has been found to be especially advantageous for the hollow cone to have an apex angle of about 154.degree..
In a special embodiment, the apertures of the cone have a total area that is about 1.5 to 3 times as large as the area of the aperture in the membrane. It has been found especially advantageous for the total area of the apertures in the cone to be about twice as large as the area of the aperture in the membrane. An excellent operating characteristic is obtained especially when the cone has only one series of concentrically disposed round or long-oval apertures.
The excellent responsiveness of the non-return valve of the invention is based especially on the proposed apex angle of the hollow cone. On the one hand, the proposed angle assures a sufficient primary bias of the basically planar membrane even after long use, resulting in a good sealing action when the pneumatic pressure is applied directly to the face of the membrane. At the same time, due to the relatively low angle bias of the membrane, the membrane effect nevertheless remains effective to a high degree, so that extremely low reaction forces applied to the underside of the membrane will suffice to lift it from the hollow cone. At the same time it is especially important that even a slight lifting of the membrane will result in a large passage cross section. Therefore, no great displacement or deformation of the membrane is needed in order to shift it from the closed to the open state. The actual elasticity of the membrane is therefore not of decisive importance, and instead the possibility is provided in accordance with the invention for selecting from the plurality of usable elastomeric materials those which are best suited for a particular application. In the introduction of fresh air for the detoxification of exhaust gases in the exhaust manifold of an internal combustion engine, it is necessary, for example, to dispose the non-return valve extremely close to the cylinder head in order to make optimum use of the injector effect of the exhaust gases. In these areas very high temperatures are produced. The use of membranes of a silicone rubber has proven excellent in this case.
Another important feature of the non-return valve of the invention is that its design permits a minimization of the mass of the moving parts of the membrane. This results in a simple maximization of the attainable operating frequencies, and levels of 200 hertz are easily achievable.